Cat's Cradle is a sci-fi novel by US author Kurt Vonnegut about a device capable to freeze all the water on Earth. The second half of the novel is set on the fictional Caribbean Island of San Lorenzo, which is heavily based on Haiti.José Eduardo González Vargas, 22 May 2009

The flag of San Lorenzo is described in the book thusly "The flag of San Lorenzo consisted of a Marine Corporal's chevrons on a royal blue field"José Eduardo González Vargas, 22 May 2009

According to wikipedia,
there is no difference in design in the US Army and Marines' Corporal's
chevrons (though to the latter are added two rifles per saltire), and
neither uses a blue background; the description above does not mention
the color of the chevrons of the flag, so I assume it is the same as in
the mentioned military rank insignia — golden yellow. The shape of this
emblem differs from regular chevrons by being slightly curved inwards.

I made a conjectural reconstruction based on the quoted description, with
the chevrons rotated to point to the fly, and throughout and centered on
a 2:3 rectangular field, making use of vexillographic trivialsAntónio Martins-Tuválkin, 30 May 2009